Tubular reactors have been in use for several years. Examples of such reactors are disclosed by U.S. Pat. No. 3,052,524 and GB932048, which describe a concentric tubular reactor consisting of three tubes, with the heat transfer fluid flowing in the most inner and most outer tubes, and with the reactant fluid flowing in the middle tube. Another example is disclosed by WO 2009150677, which shows a three concentric tube system for catalytic reactions.
Traditional concentric tubular reactors have a constant profile, i.e. the flow path is straight, in both the process and utility sides. This means that the flow within the tubular reactor, on both sides, is often laminar, particularly at lower flow rates, which are commonly employed on the process side when reactions take many seconds up to several minutes to complete.
Operating in the laminar flow regime provides:                Poor Mixing        Poor Heat Transfer (unless the distance between the walls is very small)        Poor Plug Flow        
This can result in reduced product yield or selectivity of the desired product, and thus the end mixture will contain undesired by-products which need to be separated from the desired product.